1. Field of the Invention
The present invention relates generally to signal measurement systems and, more particularly, providing a magnified view of displayed waveforms in signal measurement systems.
2. Related Art
Conventional signal measurement systems such as digital oscilloscopes sample, record and display time-varying analog signals. Samples of an input signal are taken and quantified, and the resultant digital representations are stored in a waveform memory under the control of a sampling clock. The acquired data may subsequently be read out as locations in memory are sequentially addressed by a clock signal to provide digital data which can be converted to a time-varying output signal for a waveform display. The sampling clock may be operated at one of several selectable rates depending upon the frequency content of the input signal. The selection of the portion of the analog input signal which is sampled and stored is determined by appropriate triggering circuitry to enable the operator to display the desired portion of the waveform.
There are many types of display elements which can be presented in signal measurement systems in general and test and measurement instruments in particular. For example, in addition to waveforms representing the signals currently received at channel inputs, waveforms referred to as function waveforms may also be displayed. Function waveforms are waveforms created by processing the signal waveforms. Function waveforms may be created, for example, by performing arithmetic manipulations or combining multiple input signal waveforms. The resulting function waveforms are placed in a system memory for subsequent retrieval and display. In addition, memory waveforms may also be displayed. Memory waveforms are waveforms which have been stored in memory for later display. In addition to the above waveforms, other well-known display elements such as marker indicators, trigger indicators, etc. are typically available for display.
Conventional test and measurement systems typically provide a display grid commonly referred to as a graticule on which the display elements are presented. The display grid divides the coordinate axes into a series of divisions. Waveforms are displayed on the graticule and are scaled vertically and horizontally to facilitate analysis. Typically, the horizontal scale represents sweep speed and is in units of seconds per division. The vertical scale represents signal amplitude and is in units of volts per division. The center of the horizontal axis represents the delay or horizontal position of the displayed waveforms and is referred to herein as horizontal offset. The center of the vertical axis represents the displayed reference voltage of the displayed waveforms and is referred to herein as vertical offset. These parameters are generally referred to as scaling parameters. Thus, there are four scaling parameters which are controlled by the operator to capture a desired portion of a waveform and to achieve a desired relative display of multiple waveforms: horizontal scale, horizontal offset, vertical scale and vertical offset.
A primary function provided of signal measurement systems in the analysis of signals is to enable an operator to magnify the displayed waveforms. Magnified views of desired regions of displayed waveforms allow an operator to easily and accurately determine relative values between the displayed waveforms. Magnified views are also a useful and productive technique for displaying details of a displayed waveform to better understand the behavior of the waveform and its correlation with measured quantities such as peak-to-peak voltage, rise-time, etc. Generally, signal measurement systems display simultaneously two views of a displayed waveform when the operator selects the magnification feature: the original or main waveform display, and the magnified waveform display. When the magnification function is invoked, the main waveform display is typically allocated a portion of the display screen while the magnified waveform display is drawn in the portion of the display screen not occupied by the main waveform display. The magnified waveform display presents a predetermined or selected portion or region of the main waveform display at some expanded scale.
In one conventional approach to providing a magnified view of waveform displays, the waveforms in the selected portion of the main waveform display are rendered in a unique color, commonly dark red. This technique derives from that used in monochrome analog oscilloscopes which used a higher intensity shade for signal waveforms in the selected waveform region. There are a number of drawbacks to such conventional systems. First, when the color of the waveforms is replaced with the selected intensified color, the informational content of the waveform display embodied in the waveform color is lost. Furthermore, it is difficult to distinguish between multiple waveforms rendered in the same intensified color. Also, changing colors of the selected region is not necessarily sufficient to identify the selected portion of the waveforms. This may occur, for example, when the magnified scale is very small relative to the main scale or when the displayed waveforms are very sparse. In such situations there may be an extremely small region rendered in the intensified trace which may be difficult or impossible for an operator to see.
Another conventional approach to providing a magnified view requires the operator to delineate the region of the main view which is to be magnified using vertical markers. This conventional technique is commonly used in monochrome oscilloscopes where the implementation of an intensified trace using different colors or shades is difficult or impossible. This approach, however, is also subject to significant drawbacks. When a large amount of waveform information is presented in the main waveform display, the vertical markers may be indistinguishable from the displayed waveforms and associated information. A large amount of waveform information may be displayed, for example, when running in an untriggered state or when using infinite persistence with multi-valued waveforms. As a result, the extent of the waveform display which is being magnified cannot be easily identified in the main waveform display. This significantly reduces the utility of the magnified waveform display.
What is needed, therefore, is a system and method for generating a magnified view of a waveform display which is graphically associated with a selected region of the main view without compromising the information presented in either view. The system should also provide the operator with the ability to directly control the extent and position of the selected region of the waveform display to be magnified. Such a system should also be simple and uncomplicated to enable an operator to perform magnification operations on displayed waveforms quickly and easily.